Wordpress subpage diepte

<?PHP
foreach ($sb_nav_page_array as $page_id) {
$sub_pages = get_pages('child_of=' . $page_id . '&sort_column=menu_order&order=desc&depth=1');
if ($sub_pages) {
$sub_page_output = '<ul class="subnav">';
foreach($sub_pages as $sub_page) :
$sub_page_output .= '<li><a href="' . get_permalink($sub_page->ID) . '">' . get_the_title($sub_page->ID) . '</a></li>';
endforeach;
$sub_page_output .= '</ul>';
} else {
$sub_page_output = "";
}

if ($sub_page_output != "") {
if (is_page($page_id) || is_subpage($page_id) || (get_option('sb_nav_blog_page_id') == $page_id && (is_home() || is_single() || is_search() || is_category() || is_tag() || is_archive()))) {
$nav_class = ' class="currentPageItem navigationDropDown"';
} else {
$nav_class = ' class="navigationDropDown"';
}
} else {
if (is_page($page_id) || (get_option('sb_nav_blog_page_id') == $page_id && (is_home() || is_single() || is_search() || is_category() || is_tag() || is_archive()))) {
$nav_class = ' class="currentPageItem"';
} else {
$nav_class = "";
}
}
?>

<div id="menu">
<ul>
<?php
wp_list_pages('title_li=&depth=2&sort_column=menu_order&sort_order=ASC');
?>
</ul>
</div>